Researchers at Florida Atlantic University (FAU) estimate there are around 15,000 sharks, most of which are lurking less than 200 yards from dry land.

“We got here this morning and they were thick, really thick,” Craig Pollock, a lifeguard at Midtown Beach told the Palm Beach Daily News on Tuesday. “They were frenzied and chasing bait all the way up to shore. They were practically right on the sand.”

Although these migrating sharks are not the most dangerous species — black-tips only account for around one-fifth of unprovoked attacks in Florida — authorities are not taking any chances. Many beaches are on high alert with double red flags warning vacationers to stay out of the water.

“Our data has shown that the bulk of the migration occurs in January and February,” Steve Kajiura, a shark researcher with FAU, told TCPalm.com. “But it may be a little behind this year due to the warmer weather and water temperatures.”